A person receives a laceration along the anterior border of the trapezius muscle in the neck and subsequently the point of his shoulder (scapula) sags and he has some difficulty fully abducting his arm. What nerve appears to have been severed?
**Core Concept:**
The trapezius muscle is a large, fan-shaped muscle on the posterior surface of the neck and upper back. It is responsible for movements of the scapula and rotation of the shoulder joint. The anterior border of the trapezius muscle has two major nerves that supply it: the cervical roots C5, C6, C7, and C8, and the thoracic root T1. These nerves are part of the brachial plexus and provide motor and sensory innervation to the trapezius muscle.
**Why the Correct Answer is Right:**
In the given scenario, the person experiences weakness in scapular upward movement (abduction) and difficulty in fully abducting the arm. This suggests that the motor function of the trapezius muscle has been compromised. The anterior border of the trapezius muscle receives motor innervation from cervical and thoracic nerves C5, C6, C7, C8, and T1. When one or more of these nerves are severed, the affected person will exhibit the described symptoms.
**Why Each Wrong Option is Incorrect:**
A. The correct answer (C5, C6, C7, C8, and T1) cannot be determined from the provided options.
B. This option is not relevant to the described symptoms and does not correspond to any specific nerve.
C. This option is not relevant to the described symptoms and does not correspond to any specific nerve.
D. This option is not relevant to the described symptoms and does not correspond to any specific nerve.
**Core Concept (Mnemonic):**
Hence, the correct answer is:
**Correct Answer:** C5, C6, C7, C8, and T1
**Clinical Pearl:** The brachial plexus is the network of nerves that innervates the upper extremity and is formed by the union of the ventral rami of cervical and thoracic spinal nerves C5 to T1. Severing any of these nerves can lead to the described symptoms, as they are crucial for the function and innervation of the trapezius muscle.